1. Field of the Invention
The present invention relates to a correcting method of an analyzer for a total reflection fluorescent X-ray.
2. Description of the Related Art
An analyzer for a fluorescent X-ray using a phenomenon in which an X-ray irradiated to a sample at a small incident angle is totally reflected on a sample surface is applied to measure minor impurity materials on the sample surface, which is optically polished.
In the total reflection fluorescent X-ray analyzer, a primary X-ray emitted from an X-ray source is reflected on a surface of a sample, for example, a surface of a semiconductor wafer. At this time, a fluorescent X-ray emitted from a portion close to the surface of the wafer, that is, a secondary X-ray is detected by a secondary X-ray detector, whereby an inner surface distribution of minor impurity material adhered to the surface of the sample.
More specifically, if an optically smooth plane is irradiate with X-ray at a small incident angle, the X-ray is reflected conformably to the incident angle without being absorbed by the sample irradiated with X-ray. In other words, the X-ray is totally reflected. At this time, if there is minor impurity material on a portion close to the plane, the X-ray does not enter the sample deeply. Due to this, the fluorescent X-ray from the sample and a scattered X-ray can be prevented, and the fluorescent X-ray from the minor impurity material can be detected with high sensitivity.
Therefore, an S/N ratio (a ratio of a signal to noise) can be sufficiently detected.
Conventionally, there have been known two types of total reflection fluorescent X-ray analyzers, that is, a total reflection fluorescent X-ray analyzer having a detector for reflected wave, and a total reflection fluorescent X-ray analyzer having no detector for reflected wave.
(a) FIG. 1 shows a simply structured total reflection fluorescent X-ray analyzer having no detector for reflected wave. FIG. 2 is a view showing an incident ray and an X-ray generated from the sample.
A primary X ray 12' generated by an anticathode 11 is made monochromatic and densified, and inputted on a sample 14 (semiconductor wafer) at a predetermined incident angle.
In a case that the incident angle .theta. of the monochromatic incident X-ray 12 to the sample 14 is sufficiently small (smaller than a total reflection critical angle .phi. (.phi.&lt;.theta.)), the fluorescent X-ray from the sample and the scattered X-ray can be almost ignored since the X-ray 12 is totally reflected as shown in FIG. 2, and a fluorescent X-ray 15 from impurity material 101 can be detected by a detector 16.
However, since this type of the total reflection fluorescent X-ray analyzer can not confirm the change of intensity of a reflected wave 17, there is a disadvantage in that the incident angle .theta. of the X-ray cannot be correctly obtained. In other words, according to this type of the total reflection fluorescent X-ray analyzer, since the total reflection critical angle .phi. of the incident X-ray is obtained by measuring the intensity of the fluorescent X-ray 15, the correct the total reflection critical angle .phi. cannot be obtained, an error of the incident angle .theta. of the X-ray is large, and the analysis of the sample cannot be correctly performed.
In a case that the incident angle .theta. of the incident x-ray 12 to the sample 14 is larger than the total reflection critical angle .phi. (.theta.&gt;.phi.), the incident X-ray 12 enters the sample 14, and a large amount of the fluorescent X-ray and scattered X-ray 18 are generated from the inside of the sample 14. Due to this, the S/N ratio extremely worsens.
(b) FIG. 4 shows the total reflection fluorescent X-ray analyzer having a detector for reflected wave.
The primary X ray 12' generated by the anticathode 11 is made monochromatic, and inputted on the sample 14 at an incident angle .theta.1. The reflected wave 17, which is reflected on the sample 14, is detected by a detector 19 for reflected wave. Therefore, this type of the total reflection fluorescent X-ray analyzer can correctly obtain the incident angle .theta.1 of the X-ray.
However, for changing the incident angle .theta.1 of the incident X-ray 12, there is needed a mechanism in which the sample 14 is inclined and a reflected angle .theta. to the sample 14 of a detector 19 for reflected wave (or an angle .theta.3 of the reflected X-ray to the incident X-ray) is adjusted with extremely high accuracy.
Therefore, there are disadvantages in which a number of parts is increased and the structure becomes complicated in order to realize the above-mentioned adjusting mechanism.
Moreover, the above type of the total reflection fluorescent X-ray analyzer can correct the geometric positional relationship among the anticathode 11, a spectrometer 13, the sample 14, and the detector 19 for reflected wave. However, the correction of the detector 16 for fluorescent X-ray and that of an irradiation position 20 of the X-ray cannot be performed.
FIG. 5 shows the relationship between the incident angle of the X-ray and the fluorescent X-ray in intensity in a case that the positional relationship between the irradiation position of the X-ray and the detector for fluorescent X-ray is correct. FIG. 6 shows the relationship between the incident angle of the X-ray and the fluorescent X-ray in intensity in a case that the positional relationship between the irradiation position of the X-ray and the detector for fluorescent X-ray is incorrect.
In other words, according to the conventional total reflection fluorescent X-ray analyzer, as shown in FIGS. 5 and 6, the distribution of intensity of the fluorescent X-ray to the incident angle shows the same curvature even if the positional relationship between the irradiation position of the X-ray and the detector for the fluorescent x-ray is shifted. Due to this, the shift of the positional relationship between the irradiation position of the X-ray and the detector for the fluorescent X-ray cannot be detected.
As mentioned above, there were conventionally two types of total reflection fluorescent X-ray analyzers, that is, a total reflection fluorescent X-ray analyzer having a detector for reflected wave, and a total reflection fluorescent X-ray analyzer having no detector for reflected wave. However, in both types of the total reflection fluorescent X-ray analyzers, there are disadvantages in which the incident angle of the X-ray cannot be accurately corrected with a simple mechanism and the shift of the positional relationship between the irradiation position of the X-ray and the detector for the fluorescent X-ray cannot be corrected.